The investigation did not reveal when the pilot consumed cocaine. Therefore, it cannot be established whether physiological factors affected the pilot's performance. Meteorological conditions were favourable for VFR flight. The aircraft was probably not affected by the weather. The witnesses observed the aircraft in straight and level cruise flight when the left wing suddenly failed. All fractures occurred as a result of instantaneous overload; examination of the ultralight systems revealed no anomalies. Consequently, the wing failure must have been caused by a pre-existing structural weakness. Although the left wing struck the surface of the water shortly before take-off, the collision did not cause the damage observed on the front spar. However, the rear wing spar could have been sufficiently deformed to cause damage to the wing structure. The aircraft had undergone repairs on several occasions following accidents. During one repair job, the left wing main spar was replaced by a spar with a diameter smaller than that specified by the manufacturer, which shortened the left wing chord. The way in which the left wing had to be assembled, given the shorter wing chord and the fact that the wing attachment points at the fuselage were not modified, could have created internal stresses in the structure. These stresses could have caused overload failure in a wing component when the left wing struck the surface of the water just before take-off, and this would have resulted in structural weakening of the left wing, leading to the in-flight failure shortly after.2.0 Analysis The investigation did not reveal when the pilot consumed cocaine. Therefore, it cannot be established whether physiological factors affected the pilot's performance. Meteorological conditions were favourable for VFR flight. The aircraft was probably not affected by the weather. The witnesses observed the aircraft in straight and level cruise flight when the left wing suddenly failed. All fractures occurred as a result of instantaneous overload; examination of the ultralight systems revealed no anomalies. Consequently, the wing failure must have been caused by a pre-existing structural weakness. Although the left wing struck the surface of the water shortly before take-off, the collision did not cause the damage observed on the front spar. However, the rear wing spar could have been sufficiently deformed to cause damage to the wing structure. The aircraft had undergone repairs on several occasions following accidents. During one repair job, the left wing main spar was replaced by a spar with a diameter smaller than that specified by the manufacturer, which shortened the left wing chord. The way in which the left wing had to be assembled, given the shorter wing chord and the fact that the wing attachment points at the fuselage were not modified, could have created internal stresses in the structure. These stresses could have caused overload failure in a wing component when the left wing struck the surface of the water just before take-off, and this would have resulted in structural weakening of the left wing, leading to the in-flight failure shortly after. 3.0 Conclusions 3.1 Findings The pilot was not licensed to fly with a passenger on board. During an attempted take-off, the left wing-tip struck the surface of the lake. The aircraft was in cruise flight when the left wing folded upward and towards the rear. All fractures occurred as a result of instantaneous overload. The left wing folded as a result of a pre-existing structural weakness. The left wing main spar had been replaced by a spar with a diameter smaller than specified by the manufacturer. The structural weakness could have been caused when the left wing-tip collided with the surface of the lake shortly before take-off. Toxicological test results revealed the presence of cocaine and cocaine metabolites in the urine of the pilot. It could not be determined whether physiological factors affected the pilot's performance. 3.2 Causes The left wing of the ultralight failed in flight as a result of a pre-existing structural weakness which could have been caused when the left wing-tip struck the surface of the water shortly before take-off. The Board has no aviation safety recommendations to issue at this time.4.0 Safety Action The Board has no aviation safety recommendations to issue at this time.